1. Field of the Invention
The present invention relates to a forced-air-cooled engine composed of a cylinder block integrated with a crankcase, which is a single block integrating a crankcase part and a cylinder part that extends aslant from the crankcase part, particularly to a cooling air guide cover for distributing the cooling air effectively to improve cooling of the engine.
2. Description of the Related Art
In a single cylinder, forced-air-cooled engine, with the air energized by the cooling fan attached to an end of the crankshaft being blown out from the opening of the fan cover, the air is guided to the cylinder and cylinder head having a plurality of cooling fins around their outer surfaces to flow through the spaces between the fins to cool the cylinder and cylinder head.
In Japanese Laid-Open Patent Application No. 2003-56408 an inclined cylinder type engine having a crankcase-integrated cylinder block is disclosed, with the cylinder block being composed of a crankcase part and a cylinder part cast in one piece. In this engine, in addition to a cylinder air-guide cover (air cover), a first exhaust air guide and a second exhaust air guide are provided for guiding the cooling air after cooling the cylinder to the carburetor to heat it in order to prevent occurrence of congelation in the carburetor.
However, the cylinder air-guide cover and exhaust air guide cover only the cylinder and cylinder head and do not cover the crankcase part to guide cooling air, and the crankcase part is cooled by natural cooling by the ambient air.
Another example of an inclined cylinder type, forced-air-cooled engine is shown in FIG. 7. In FIG. 7, a cylinder block 3 is a cast unit with a cylinder part 7 and a crankcase part 3A cast integrally, the cylinder part 7 extending aslant from the crankcase part 3A. A cylinder head 101 is attached on top of the cylinder part 7. A valve drive mechanism is provided on the cylinder head and covered by a cylinder head cover.
Reference numeral 103 is an exhaust outlet of the cylinder head 101, 104 is an ignition plug, 105 is a cylinder air-guide cover, 106 is a fuel hose connecting a fuel tank (not shown in the drawing) to a fuel filter (not shown in the drawing). Reference numeral 3a indicates a root part of the cylinder part 7 (connection part of the cylinder part to the crankcase part). Reference numeral 4 is an output shaft of a crankshaft, a cooling fan (not shown in the drawing) being attached to the end opposite to the output shaft 4 (front side) of the crankshaft. A fan cover covering the cooling fan is provided in its back plate with a secondary blow-out opening 1b and a main blow-out opening (not visible in the drawing) for blowing out air energized by the cooling fan. Cooling air 5 blown out from the main blow-out opening hits the cylinder part and cylinder head and is guided by the cylinder air-guide cover to flow through spaces between cooling fins thereof to cool them and flow out into ambient air. Cooling air 6 blown out from the secondary blow-out opening 1b hits a part 3b of a side wall of the crankcase part 3A, cools the part 3b of the crankcase part 3A, and diffuses into the ambient air. Therefore, the crankcase part is cooled only locally, and most of the crankcase part is left to be cooled naturally by the ambient air. As mentioned above, in an engine of this kind, priority is put on cooling the cylinder and cylinder head, and generally positive cooling of the crankcase part is not considered, although in the case of the example a part of the crankcase part is cooled by hitting the cooling air blown out from the secondary blow-out opening.
In engines of this kind, lube oil is accumulated inside the crankcase part 3A and splash lubrication is adopted, that is, the lube oil in the crankcase part 3A is splashed by means of a projecting portion provided to the connecting rod, and oil cooler is not provided. Cooling of lube oil is usually left to natural cooling via the crankcase part.
However, the amount of heat generated increases and the surface from which to release heat decreases as engines of this kind are small sized and high powered, so lube oil temperature tends to become higher. Particularly, under a high temperature environment, the temperature of lube oil rises excessively and durability of the engine is deteriorated. Further, in recent years, many component parts made of plastic material are used for weight saving, for facilitating manufacturing, and for cost saving, so it is required to lower the temperature of the surface of the engine as far as possible to evade an excessive temperature rise of these parts.
In engines of this kind, a fuel hose connecting a fuel tank mounted on top of the engine to a fuel filter mounted in a lower part of the engine often passes a space behind the cylinder part downstream of the cooling air flow. In this case, the fuel hose is heated by the cooling air increased in temperature by cooling the engine, and vapor lock tends to occur in the fuel hose. To prevent this, a heat shield plate is often provided between the fuel hose and the cylinder part. The fuel hose is usually made of elastic material and it shakes due to vibration and/or shaking of the engine, so it often happens that the fuel hose contact with adjacent parts relatively increased in temperature by the exhausting cooling air and damaged. When the fuel hose is damaged, fuel leaks and fire may occur. As a means to fix a fuel hose, Japanese Laid-Open Utility Model Application discloses a groove of semi-circular cross section for receiving the fuel hose on the end face of the crankcase part and cover the fuel hose by a hose cover.
However, with this art, it is not easy to form a groove of semi-circular cross section on the end face of the crankcase part.